THERMODYNAMIC MODELLING OF C-O-H FLUIDS

Abstract

H2O, CO2, CH4, CO, H2 and O2 are the most important species in crustal fluids. The composition of these C-O-H fluids can be calculated if the pressure, temperature, carbon activity, and either the oxygen fugacity or the atomic H/O ratio of the fluid is known. The calculation methods are discussed and calculation results are illustrated with isobaric T-Xi, P-T, and isobaric-isothermal ternary C-O-H diagrams. Fluid inclusion compositions, in particular, the XCO2/(XCO2+XCH4) ratio, can be used for C-O-H model calculations. However, care should be taken about possible post-entrapment changes, which may have modified the chemical composition of the fluid inclusion.